Inorganic compound containing active oxygen and process for producing the same

ABSTRACT

The present invention relates to an active oxygen developing substance composed of an aluminosilicate obtained by heating hydrogarnet as a precursor substance at 700° C. or higher; an aluminosilicate catalyst supporting cobalt oxide, produced by supporting cobalt oxide on the surface of the aluminosilicate; a method for manufacturing these; and applications of these as oxidation catalysts, solid electrolytes, oxygen occlusion carriers, and so forth.

TECHNICAL FIELD

This invention relates to a method for manufacturing an inorganiccompound including active oxygen, and more particularly relates to anovel active oxygen developing substance including or occluding both asuperoxide anion (O₂ ⁻) and a peroxide anion (O₂ ²⁻), and to a methodfor manufacturing this substance, and applications therefor. Inorganiccompounds including or occluding both a superoxide anion and a peroxideanion were not known in the past, but the present invention is useful inthat it provides a novel material that includes or occludes both ofthese.

The active oxygen developing substance of the present invention isuseful as a constituent component of oxidation catalysts, solidelectrolyte fuel-cell electrodes, antimicrobial agents, ion conductors,and so forth, and a molded article of the active oxygen developingsubstance of the present invention, is useful in that it provides a newtype of exhaust gas purification catalyst for two-wheeled vehicles, asolid electrolyte for secondary cells, an oxygen occlusion carrier, orthe like.

The present invention also relates to an aluminosilicate catalystsupporting cobalt oxide, to a method for manufacturing this catalyst,and to applications for this catalyst, and more particularly relates toa new aluminosilicate catalyst supporting cobalt oxide that has moreactive oxidation capability at lower temperatures than conventionaloxidation or combustion catalysts, and to a method for manufacturingthis catalyst, to a method for the oxidative decomposition of volatileorganic compounds with this catalyst, and so forth. The novelaluminosilicate that is the catalyst component of the present inventionhas a zeolite-like structure in which active oxygen (superoxide: O₂ ⁻,peroxide: O₂ ²⁻) is encapsulated, and can be used in oxidation reactionsof hydrocarbons and the like by means of the active oxygen included inthe structure. Examples of such reactions include epoxidation, completeoxidation, partial oxidation, and coupling. When cobalt oxide issupported on this novel aluminosilicate, the result is a catalyst ofeven higher activity, and the aluminosilicate catalyst supporting cobaltoxide of the present invention can be utilized in a wide range oftechnological fields dealing with the environment, energy, the chemicalindustry (manufacturing process), and so forth. Further, a formed ormolded article of the aluminosilicate supporting cobalt oxide of thepresent invention is useful, for example, in that it provides a new typeof exhaust gas purification catalyst for two-wheeled vehicles, a solidelectrolyte for secondary cells, an oxygen occlusion carrier, or thelike.

BACKGROUND ART

As air pollution has worsened around urban centers, standards aimed atsignificantly cutting back nitrogen oxides, which are a cause ofrespiratory problems, and hydrocarbons, which are a cause ofphotochemical smog, have been established by the Central EnvironmentCouncil of the Ministry of the Environment, as announced in 2004 on thebasis of the Air Pollution Control Law. More specifically, exhaust gasrestrictions on motorcycles and other two-wheeled vehicles are scheduledto be greatly tightened in 2006-2007 and beyond. As an example of thenew standards, it is planned that as of 2006, scooters of 50 cc orsmaller must emit no more than 0.5 g of hydrocarbons per kilometer oftravel (a reduction of 75% over the current level), and no more than0.15 g of nitrogen oxides (50% reduction). For motorcycles over 250 cc,it is planned that as of 2007, they must emit no more than 0.3 g ofhydrocarbons (85% reduction) and no more than 0.15 g of nitrogen oxides(50% reduction).

Hydrocarbons are emitted as a result of incomplete combustion ofgasoline, and their emission by two-wheeled vehicles is more than tentimes that by passenger vehicles, accounting for some 20% of the totalemissions of four- and two-wheeled vehicles combined. Given thissituation, the use of the same catalytic converters in two-wheeledvehicles as those used in passenger vehicles has been studied, butexisting catalytic converters would be disproportionately costly oninexpensive two-wheeled vehicles, and a less expensive exhaust gaspurification catalyst needs to be developed.

In today's automobile catalytic converters, platinum, palladium,platinum/rhodium, palladium/rhodium, platinum/palladium/rhodium, and thelike are supported on a monolithic carrier made from cordierite, andused as a three-way catalytic converter. Further, ceria, which is anoxygen-storing substance, has been used as an auxiliary catalyst inorder to absorb fluctuations in the air-fuel ratio. The above noblemetals have high catalytic activity, but they are costly, and moreoverneed to be used in large quantities, so they are recovered and reused.

An example of substances known and put to use in the past as activeoxygen developing substances is a photocatalyst typified by titaniumoxide. Electrons and holes are formed when light (UV rays) is absorbedby titanium oxide. Because the oxidative strength resulting from holesis greater than the reductive strength resulting from excited electronswith titanium oxide, adsorbed water on the catalyst surface is oxidizedby the holes, producing hydroxy radicals (.OH). Meanwhile, a reactionproceeds in which the oxygen in the air is reduced, producing activeoxygen (O₂ ⁻). It is believed that active oxygen becomes water viahydrogen peroxide (H₂O₂) or the formation of a peroxide of anintermediate of the oxidation reaction. There are also cases in whichactive oxygen acts directly on carbon-carbon bonds and decomposesharmful organic substances.

Another substance known to develop active oxygen is a 12CaO.7Al₂O₃compound that encloses active oxygen species (Japanese Laid-Open PatentApplication No.2002-3218). This 12CaO.7Al₂O₃ compound is manufacturedfrom a raw material mixture of calcium and aluminum in an atomicequivalent ratio of 12:14, which are subjected to solid phase reactionin a dry oxidative atmosphere controlled to an oxygen partial pressureof at least 10⁴ Pa, and preferably at least 10⁵ Pa, and a water vaporpartial pressure of no more than 1 Pa, and at a high firing temperatureof at least 1200° C., and preferably 1300° C. The active oxygen enclosedby a 12CaO.7Al₂O₃ compound manufactured in an atmosphere in which theoxygen partial pressure and water vapor partial pressure are strictlymanaged, which requires a large quantity of thermal energy, is O₂ ⁻and/or O⁻.

However, when it came to this type of active oxygen developingsubstance, no inorganic compound that would include or occlude both asuperoxide anion (O₂ ⁻) and a peroxide anion (O₂ ²⁻) was known up tonow, and all that was known was the production of a superoxide with a12CaO.7Al₂O₃ compound or a photocatalyst such as the above-mentionedtitania.

Furthermore, the release of volatile organic compounds and the like intothe atmosphere today is causing serious environmental pollution.Combustion is one way that volatile organic compounds can be removed,but this requires high temperatures over 1000° C. Catalysts are utilizedto allow combustion to occur at lower temperatures. The catalysts usedfor such applications are called combustion catalysts. In the past,oxides of cobalt, copper, manganese, chromium, and the like have beensupported on porous alumina, allowing the combustion temperature to belowered to between 300 and 600° C. (see, for example, (1) Y. M. Kang andB. Z. Wan, Appl. Cat. A, Vol. 114 (1994), p. 35, (2) R. S. Drago, K.Jurczyk, D. L. Singh, and V. Young, Appl. Cat. B8 (1996), p. 155, and(3) N. Watanabe, H, Yamashita, H. Miyadera, and S. Tominaga, Appl. Cat.B8 (1996), p. 405). Today, however, the development of a catalyst withhigher activity than conventional catalysts is needed for the sake ofenergy conservation. Catalysts supporting noble metals such as platinum,palladium, and rhodium have high activity and are commonly used inautomobile catalytic converters. Although these noble metals have highcatalytic activity, they are also valuable and costly, and are used inlarge quantities, and therefore are recovered and reused. Hydrocarbons,which are environmental pollutants emitted from internal combustionengines, are emitted as a result of the incomplete combustion ofgasoline, and their emission by two-wheeled vehicles is more than tentimes that by passenger vehicles, accounting for some 20% of the totalemissions of four- and two-wheeled vehicles combined. Given thissituation, the use of the same catalytic converters in two-wheeledvehicles as those used in passenger vehicles has been studied, butexisting catalytic converters would be disproportionately costly oninexpensive two-wheeled vehicles, and a less expensive exhaust gaspurification catalyst that does not make use of noble metals needs to bedeveloped in this field of technology.

DISCLOSURE OF THE INVENTION

In light of the above situation, and the prior art discussed above, theinventors conducted diligent research aimed at developing a novel activeoxygen developing substance that would be capable of including oroccluding in its structure O₂ ²⁻ having greater oxidative strength thanactive oxygen species such as O₂ ⁻ and O⁻ known to be developed byphotocatalysts such as titania or by a 12CaO.7Al₂O₃ compound. As aresult, they arrived at the present invention upon discovering that analuminosilicate expressed by Ca₁₂(Al_(14−X)Si_(X)) O_(33+0.5X) includesor occludes both a superoxide anion (O₂ ⁻) and a peroxide anion (O₂ ²⁻).

It is an object of the first aspect of the present invention to providea novel active oxygen developing substance that includes or occludesboth a superoxide anion (O₂ ⁻) and a peroxide anion (O₂ ²⁻), which arepowerful oxidants, and a method for manufacturing the active oxygendeveloping substance.

It is another object of the present invention to provide a novel activeoxygen developing substance wherein active oxygen such as O₂ ²⁻ isincluded or occluded in the structure of the substance.

It is another object of the present invention to provide analuminosilicate which is a novel active oxygen developing substance thatincludes or occludes both a superoxide anion (O₂ ⁻) and a peroxide anion(O₂ ²⁻) in its structure.

It is another object of the present invention to produce a formed ormolded article of an aluminosilicate which is a novel active oxygendeveloping substance, and provide a member such as an exhaust gaspurification catalyst for two-wheeled vehicles and the like, a solidelectrolyte for secondary cells, or an oxygen occlusion carrier.

In the course of further diligent research aimed at developing acatalyst of higher activity in light of the above prior art, theinventors took a close look at hydrogarnet, whereupon they discoveredthat when it is heated to 350° C. or higher, it changes into analuminosilicate, and this aluminosilicate includes or occludes activeoxygen such as peroxide anions and superoxide anions into its structure.These active oxygens stay in the structure at room temperature, but canmove at temperatures over 400° C. Specifically, the active oxygenpresent in the structure fly out of the structure and induce chemicalreactions such as oxidation. The inventors arrived at the presentinvention upon discovering for the first time that after the activeoxygen moves, the oxygen in the air is taken into the structure,regenerating it, and that active oxygen can be supplied continuously andincessantly, and that active oxygen is a powerful oxidant and isextremely effective in the oxidative decomposition or combustion ofvolatile organic compounds and so forth, and when cobalt oxide, whichhas long been known as an oxidation catalyst, is supported on analuminosilicate that develops active oxygen, even higher oxidationcapability can be imparted at low temperature.

It is an object of the second aspect of the present invention to developand provide a catalyst with higher activity than conventional oxidationor combustion catalysts, and to provide a method for manufacturing thiscatalyst. It is a further object of the present invention to create amolded article of an aluminosilicate supporting cobalt oxide, andprovide an exhaust gas purification catalyst for two-wheeled vehiclesand the like, a combustion exhaust gas purification catalyst, an oxygenocclusion member, or the like.

The first aspect of the present invention will now be described infurther detail.

The method of the present invention for manufacturing a novel activeoxygen developing substance does not require control of the oxygenpartial pressure or water vapor partial pressure, and the heating may beat a relatively low temperature of 1000° C or lower. An example of thismanufacture will now be given, but the method of the present inventionfor manufacturing a novel active oxygen developing substance is notlimited to just the following method. The active oxygen developingsubstance of the present invention is manufactured by using hydrogarnetas a precursor substance, and heating it to at least 700° C. in anelectric furnace or the like under an air atmosphere. The chemicalcompositional formula of the hydrogarnet used as the precursor isCa₃Al₂(SiO₄)_(3−Y)(OH)_(4Y), where the value of Y is in the range of0≦Y<3.

Meanwhile, the chemical compositional formula of the aluminosilicatehaving a novel active oxygen developing function isCa₁₂(Al_(14−X)Si_(X))O_(33+0.5X), where the value of X is in the rangeof 0<X≦4. The chemical composition when X=4 is Ca₁₂(Al₁₀Si₄)O₃₅, andwhen Ca₁₂(Al₁₀Si₄)O₃₅ is synthesized, the composition of the precursorhydrogarnet is Ca₃Al₂(SiO₄)_(0.8)(OH)_(8.8) (Y=2.2). The hydrogarnet issynthesized as follows. First, a calcia source, an alumina source, and asilica source are mixed so as to match the hydrogarnet composition, thatis, the composition of hydrogarnet with the desired Y value, and anexcess of water is added to this to prepare a mixture.

The calcia source here can be slaked lime, unslaked lime, calciumcarbonate, gypsum, or the like; the alumina source can be kaolin,alumina sol, boehmite, aluminum hydroxide, aluminum oxide, or the like;and the silica source can be kaolin, silica, amorphous silica,diatomaceous earth, silica sand, quartz, or the like. The preparedmixture is subjected to a wet heat treatment in an autoclave for atleast 5 hours at a temperature of from 100 to 200° C. to synthesizehydrogarnet. The reaction will not proceed adequately if the temperatureis below 100° C., but too much thermal energy will be consumed if thetemperature is over 200° C. The heating time can be shorter than 5hours, but at least 5 hours is preferable in order to obtain hydrogarnetwith good crystallinity.

An aluminosilicate that is a novel active oxygen developing substancecan be obtained by heating hydrogarnet to 700° C. or higher and 1200° C.or lower in an air atmosphere. Heating at a temperature under 700° C. isundesirable because pyrolysis will be inadequate. The heating may beperformed at an even higher temperature, but this will consume too muchthermal energy, so the limit is set at 1200° C. or lower. Analuminosilicate that is the novel active oxygen developing substance ofthe present invention can be obtained by heating hydrogarnet synthesizedby the above method. Cases in which X=4 and X=2 are given below asexamples.

The compositional formula of the precursor hydrogarnet used tosynthesize Ca₁₂Al₁₀Si₄O₃₅ (X=4) is Ca₃Al₂(SiO₄)_(0.8)(OH)_(8.8) (Y=2.2),and the pyrolysis thereof that occurs at 700° C. is expressed asfollows.5Ca₃Al₂(SiO₄)_(0.8)(OH)_(8.8)→Ca₁₂Al₁₀Si₄O₃₅+3CaO+22H₂O

The compositional formula of the precursor hydrogarnet used tosynthesize Ca₁₂Al₁₂Si₂O₃₄ (X=2) is Ca₃Al₂(SiO₄)_(1/3)(OH)_(32/3)(Y=8/3), and the pyrolysis thereof that occurs at 700° C. is expressedas follows.6Ca₃Al₂(SiO₄)_(1/3)(OH)_(32/3)→Ca₁₂Al₁₂Si₂O₃₄+6CaO+32H₂O

The Ca₁₂Al₁₀Si₄O₃₅, Ca₁₂Al₁₂Si₂O₃₄, and so forth obtained from the abovereaction formulas are examples of aluminosilicates that are the novelactive oxygen developing substance of the present invention. The novelactive oxygen developing substance of the present invention is obtainedwithin the range of 0<X≦4, and is produced by the pyrolysis ofhydrogarnet, which is a precursor thereof. As can be seen from thepyrolysis formulas, unslaked lime (CaO) is admixed as a by-product, butunslaked lime does not participate in the development or inclusion ofactive oxygen. CaO can be easily removed by dissolving it with a diluteacid such as hydrochloric acid or nitric acid.

ESR measurement and Raman spectroscopy are two ways to check whether ornot the hydrogarnet pyrolyzate, that is, the aluminosilicate that is thenovel active oxygen developing substance, includes or occludes activeoxygen such as superoxide anions (O₂ ⁻) and peroxide anions (O₂ ²⁻). Forinstance, the results of ESR and Raman spectroscopy at room temperaturefor the Ca₁₂Al₁₀Si₄O₃₅ used in the working examples given below will nowbe described. First, FIG. 1 shows the ESR measurement results. Thespectrum appearing at g₁=2.049 mT indicates the presence of superoxideanions. FIG. 2 shows the results of Raman spectroscopy at roomtemperature. Just as in ESR measurement, the presence of superoxideanions is confirmed from a peak at 1075 cm⁻¹.

The results in both FIGS. 1 and 2 tell us that Ca₁₂Al₁₀Si₄O₃₅ isincluded or occluded in the structure of the superoxide anions.Furthermore, Raman spectroscopy results for Ca₁₂Al₁₀Si₄O₃₅ reveal adistinct peak at 853 cm⁻¹ as well as at 1075 cm⁻¹. The formercorresponds to a peak originating in peroxide anions, and the latter insuperoxide anions. The above results lead to the conclusion that thenovel active oxygen developing substance of the present inventionincludes or occludes superoxide anions and peroxide anions in itsstructure.

FIG. 3 shows the crystal structure of Ca₁₂Al₁₀Si₄O₃₅. The structure ofCa₁₂Al₁₀Si₄O₃₅ is a cubic system, with a lattice constant of a=12.0116Å, and a space group of I⁻43d. This is a zeolite-like structure in which(Al,Si)O₄ tetrahedra are formed in the form of a framework, and activeoxygen O₂ ⁻ and O₂ ²⁻ are present in the voids (spaces of about 4 Å) inthis framework.

The active oxygen included or occluded by the aluminosilicate that isthe novel active oxygen developing substance of the present invention isa powerful oxidant, is discharged from within the structure when heatedto 400° C. or higher, and participates in chemical reactions and soforth. In other words, the active oxygen included or occluded by thealuminosilicate that is the novel active oxygen developing substance ofthe present invention is able to move at a temperature of 400° C. orhigher. For instance, the novel active oxygen developing substance hasthe ability to completely oxidize and decompose volatile organiccompounds (VOCs) into CO₂ or H₂O at a low temperature of 400 to 600° C.Because of this, the active oxygen developing substance of the presentinvention can be used as the active component of an oxidation catalyst.

The active oxygen in the structure is gradually consumed as an oxidativedecomposition reaction continues under an oxygen-free atmosphere, and ifthe reaction continues long enough, the active oxygen is completely usedup, after which no more is supplied. However, if air or oxygen issupplied to the novel active oxygen developing substance after activeoxygen ceases to be supplied, active oxygen will be produced again inthe structure and the powerful oxidizing action will be restored. Thisis a distinctive feature of this substance. FIG. 4 shows experimentalresults. Therefore, if air or oxygen is continually supplied during theoxidative decomposition of VOCs and the like, the supply of activeoxygen from the novel active oxygen developing substance will never runout.

Because superoxide anions and peroxide anions both have a powerfuloxidizing action, they are able to decompose VOCs and other harmfulchemical substances, and hold promise in applications such as theoxidative decomposition of these harmful chemical substances in theenvironmental field. Furthermore, the consumed active oxygen (superoxideanions and peroxide anions) is regenerated in the structure of the novelactive oxygen developing substance of the present invention, andtherefore this substance has the advantage that it can be usedindefinitely.

The novel active oxygen developing substance of the present inventionhaving the above advantages can be obtained as a powder in itsmanufacturing method. In addition to utilizing this substance as apowder, many other conveniences and new functions as a molded articlewill likely be realized. The form of the molded article will bedetermined by the intended use, and the molding method can be any onethat is used in the manufacture of molded ceramics. Possible forms ofthe molded article include granules, a sheet, a rod, a tube, hollowfibers, a monolith, and a honeycomb, and examples of molding methodsinclude casting, press molding, dry CIP molding, injection molding, andsheet molding. Naturally, whether the molded article will be solid orporous is taken into account along with the desired form in molding. Asan example, of the various molded articles that are possible, thefollowing is a description of the oxidation catalyst function of samplesin the form of pellets and sheets.

FIG. 5 is a simplified view of the measurement apparatus used to examinethe oxidation catalyst performance of the substance of the presentinvention. This apparatus consists of (1) a gas supply unit, (2) aheating unit, and (3) a gas analysis unit. The gas supply unit suppliesthe hydrocarbons to be subjected to oxidative decomposition, and the airor oxygen used as a combustion auxiliary. The heating unit heats areaction tube filled with the sample to a specific temperature. The gasanalysis unit analyzes the composition of the supply gas that has passedthrough the sample. The reaction tube is modified according to the formof the sample, and FIG. 6 shows a simplified example thereof. For asample in the form of a powder, pellets, or granules (4), the center ofa silica glass reaction tube (5) is packed with the sample, and the endsof the sample are held in place with rock wool (6). For a sample in theform of a sheet (7), the ends of the sheet are held in place with silicaglass tubes (8) via a sealant, and the silica glass tubes are fixed tothe sample sheet.

The oxidation catalyst function of a powder and a molded article wasexamined for propylene, benzene, and methane, which revealed that all ofthese hydrocarbons are decomposed at a temperature of 400° C. or higher.

The function of the novel active oxygen developing substance of thepresent invention as an ion conductor will also be described. Aconductive material and a binder were mixed intoCa₁₂(Al_(14−X)Si_(X))O_(33+0.5X) (the powdered substance of the presentinvention; 0<X≦4) to prepare a mix in the form of a paste, and this wasuse to coat the surface of an aluminum foil collector to produce anelectrode. The conductive material is used to ensure electricalconductivity, and can be, for example, carbon black, acetylene black,graphite, or the like, either singly or in mixtures of two or morematerials. The binder is used to bind the conductive material particlestogether with the powdered substance of the present invention, and canbe, for example, Teflon®, polytetrafluoroethylene, polyvinylidenefluoride, or a fluororubber. An electrode coated with the substance ofthe present invention is disposed across from a metallic lithium with aseparator (nonwoven cloth) in between. For instance, a constant currentof 0.1 mA/cm² was allowed to flow for a specific length of time up to4.5 V between the metallic lithium and the electrode in an organicsolvent containing a lithium salt, after which the substance of thepresent invention was recovered and washed and its composition examinedand found to be LiyCa₁₂(Al_(14−X)Si_(X))O_(33+0.5X) (where 0<y≦30),which confirmed that the substance of the present invention had thecharacteristics of lithium ions being inserted.

The present invention relates to an aluminosilicate having azeolite-like structure in which active oxygen (superoxide: O₂ ⁻,peroxide: O₂ ²⁻) is encapsulated, and more specifically, to a novelactive oxygen developing substance and a molded article thereof. Theeffects of the present invention are (1) the active oxygen included oroccluded in the structure produces a hydrocarbon oxidation reaction(such as epoxidation, complete oxidation, partial oxidation, andcoupling), and the novel aluminosilicate catalyst supporting cobaltoxide of the present invention can be utilized in a wide range oftechnological fields dealing with the environment, energy, the chemicalindustry (manufacturing process), and so forth, and (2) the moldedinorganic compound of the present invention is useful, for example, asan exhaust gas purification catalyst for two-wheeled vehicles, a solidelectrolyte for secondary cells, an oxygen occlusion carrier, and so on.

The second aspect of the present invention will now be described infurther detail.

The novel catalyst of the present invention can be produced by using analuminosilicate as a support, and supporting microparticles of cobaltoxide on the surface of this aluminosilicate. This aluminosilicate has acompositional formula of Ca₁₂(Al_(14−X)Si_(X))O_(33+0.5X), and the valueof X in the compositional formula is in the range of 0≦X≦4. An exampleof the supporting method is to immersion the aluminosilicate in a cobaltnitrite aqueous solution and perform evaporative drying. When thepowdered substance thus obtained is heated to 600° C. or higher, thecobalt nitrate supported on the aluminosilicate surface decomposes intocobalt oxide, creating an aluminosilicate catalyst supporting cobaltoxide. With the method of the present invention, nickel oxide, ironoxide, or another metal oxide can be used instead of cobalt oxide, forexample.

Further, the novel catalyst of the present invention is obtained bysynthesizing cobalt-containing hydrogarnet as a precursor substance by awet heat method, and heating this product at 300° C. or higher. Thechemical composition thereof is expressed by(Ca_(3−Y)CO_(Y))Al₂(SiO₄)_(3−Z)(OH)_(4Z). The novel catalyst of thepresent invention is characterized in that the Y value in thecompositional formula is in the range of 0<Y≦0.10, and Z in the range of0≦Z≦2.2. The novel catalyst of the present invention can be utilized asan oxidation catalyst or the like.

The aluminosilicate catalyst supporting cobalt oxide of the presentinvention is manufactured by synthesizing a cobalt-containinghydrogarnet in which some of the Ca²⁺ ions (a constituent element ofhydrogarnet) have been replaced with Co²⁺ ions, and then heating anddecomposing this product. To facilitate an understanding of thefollowing description, hydrogarnet itself will first be described.Hydrogarnet has a garnet structure, and its compositional formula isCa₃Al₂(SiO₄)_(3−Y)(OH)_(4Y). The value of Y here is in the range of0≦Y≦3. The compositional formula of hydrogarnet varies with the Y value.For instance, the formula is Ca₃Al₂(SiO₄)₃ when Y=0,Ca₃Al₂(SiO₄)_(1.5)(OH)₆ when Y=1.5, Ca₃Al₂(SiO₄)_(0.8)(OH)_(8.8) whenY=2.2, and Ca₃Al₂(OH)₁₂ when Y=3. The Ca²⁺ ions in the hydrogarnetstructure can be substituted with other cations of similar ion radius,such as Co²⁺ ions.

The radius of Ca²⁺ and Co²⁺ ions is 0.112 and 0.090 nm, respectively,with the latter being slightly smaller. Therefore, when Ca²⁺ ions aresubstituted with Co²⁺ ions, the lattice constant of the hydrogarnetbecomes somewhat smaller. There is a limit to the amount of substitutionof Ca²⁺ ions versus Co²⁺ ions, and when this limit was calculatedexperimentally, it was found to be Co/Ca=0.0344 (=0.10/2.90 molarratio). When the Co/Ca molar ratio is 0.0344, the compositional formulaof hydrogarnet is (Ca_(2.9)Co_(0.1))Al₂(SiO₄)_(3−Y)(OH)_(4Y). The addedamount of cobalt may be increased, but as discussed below, thisdecreases catalyst activity, so it is better not to add too much cobalt(so that the Co/Ca molar ratio would be over 0.0344).

The method for manufacturing the aluminosilicate catalyst supportingcobalt oxide of the present invention will now be described, but this isnot intended to limit the method for manufacturing the aluminosilicatecatalyst supporting cobalt oxide of the present invention. Thecobalt-containing hydrogarnet used as a precursor of the aluminosilicatecatalyst supporting cobalt oxide is prepared as follows. First, a cobaltsource, a calcia source, an alumina source, and a silica source aremixed so as to match the hydrogarnet composition, that is, thecomposition of cobalt-containing hydrogarnet with the desired X and Yvalues, and an excess of water is added to this to prepare a mixture.The cobalt source here can be cobalt hydroxide, cobalt oxide, or thelike; the calcia source can be slaked lime, unslaked lime, calciumcarbonate, gypsum, or the like; the alumina source can be kaolin,alumina sol, boehmite, aluminum hydroxide, aluminum oxide, or the like;and the silica source can be kaolin, silica, amorphous silica,diatomaceous earth, silica sand, quartz, or the like. These are not theonly sources that can be used, however, and any that have the sameeffect as these can also be used. The combined amount of cobalt andcalcium is set to be “3” in the compositional formula(Ca_(3−X)Co_(X))Al₂(SiO₄)_(3−Y)(OH)_(4Y). Preferably, the range is0<X≦0.10. The Y value is preferably in the range of 0≦Y≦2.2.

The prepared mixture is subjected to a wet heat treatment in anautoclave for at least 5 hours at a temperature of from 100 to 200° C.to synthesize cobalt-containing hydrogarnet. The reaction will notproceed adequately if the temperature is below 100° C., but too muchthermal energy will be consumed if the temperature is over 200° C., so100 to 200° C. is the preferred range. The heating time can be shorterthan 5 hours, but at least 5 hours is preferable in order to obtaincobalt-containing hydrogarnet with good crystallinity. Further, analuminosilicate catalyst supporting cobalt oxide in which the cobaltoxide is highly dispersed can be manufactured by heating thecobalt-containing hydrogarnet to between 300° C. and 1000° C. in an airatmosphere. The decomposition of the cobalt-containing hydrogarnet willbe inadequate if the heating is at a temperature below 300° C., andwhile the heating may be performed at a temperature over 1000° C., thisis undesirable from the standpoint of conserving energy.

The ion used for substitution need not be limited to cobalt, and anyother ion that can be substituted may be used instead. It is well knownthat a high-performance catalyst in which the catalyst particles arehighly dispersed can be synthesized by substituting metal ions in thecrystal structure and pyrolyzing. This catalyst manufacturing method isa proven technology in the case of using a layered double hydroxide(LDH) as a catalyst precursor (see, for example, F. Cavani, F. Trifiro,and A. Vaccari, Catal. Today, Vol. 11 (1991), p. 173; B. Chen and J. L.Falconer, J. Catal., Vol. 144 (1993), p. 214; S. Velu, R. Veda, A.Ramani, B. M. Chenda, and S. Sivasanker, Chem. Commun. (1997), p. 2107;S. Velu, K. Suzuki, M. P. Kapoor, F. Ohashi, and T. Osaki, Appl. Catal.A, Vol. 213 (2001), p. 47; and S. Velu, K. Suzuki, and T. Osaki, Catal.Let., Vol. 69 (2000), p. 43), but the inventors of the present inventionare the first to discover the catalyst of the present invention in whicha cobalt-containing hydrogarnet having a garnet structure is used as acatalyst precursor, and the method for manufacturing this substance.

Next, the amount of Co²⁺ ions that can be substituted in thishydrogarnet with the method of the present invention will be described,using as an example a hydrogarnet in which Y=2.2. FIG. 8 shows the XRDresults for cobalt-containing hydrogarnet synthesized by the abovemethod, with the Co/Ca ratio varied from 0 to 0.0714. In FIG. 8, thewhite circles are the diffraction peaks originating in hydrogarnet(Ca₃Al₂(SiO₄)_(0.8)(OH)_(8.8)), the black circles are those originatingin cobalt-containing hydrogarnet((Ca_(3−X)Co_(X))Al₂(SiO₄)_(0.8)(OH)_(8.8)), and the triangles are thoseoriginating in cobalt oxide (Co₃O₄). Hydrogarnet alone was synthesizedfor the sample with no added cobalt (Co/Ca=0). It was confirmed thatwhen some of the calcium was substituted with cobalt (Co/Ca=0.0169), thelattice constant was smaller, so the diffraction line angle shiftedhigher, producing cobalt-containing hydrogarnet. When the amount ofadded cobalt was increased to Co/Ca=0.0380, there was precipitation ofcobalt oxide that could not be substituted.

Therefore, the limit to the amount of cobalt that can be substituted isCo/Ca=0.0344. As mentioned above, the compositional formula here is(Ca_(2.9)Co_(0.1))Al₂(SiO₄)_(0.8)(OH)_(8.8). The results in FIG. 8 wereused to plot the graph of FIG. 9, which shows the relationship betweenlattice constant and Co/Ca ratio. Up to a Co/Ca ratio of 0.0344, thelattice constant steadily decreases from 1.2408 nm to 1.2313 nm, afterwhich it remains at 1.2313 nm until the Co/Ca ratio is 0.0714. Thismeans that all of the Co²⁺ ions added are being used in substitution upto a Co/Ca ratio of 0.0344, and that beyond this ratio (that is, whenthe Co/Ca ratio is over 0.0344), no substitution is being performed. Theabove results are compiled in Table 1.

TABLE 1 Lattice constants of cobalt-containing hydrogarnet[(Ca_(3−X)Co_(X))Al₂(SiO₄)_(0.8)(OH)_(8.8): 0 ≦ X ≦ 0.10] Co/Ca XCompositional formula a/nm V/nm³ 0 0 Ca₃Al₂(SiO₄)_(0.8)(OH)_(8.8)1.24078(15) 1.910 0.0101 0.03(Ca_(2.97)Co_(0.03))Al₂(SiO₄)_(0.8)(OH)_(8.8) 1.23563(6) 1.886 0.01690.05 (Ca_(2.95)Co_(0.05))Al₂(SiO₄)_(0.8)(OH)_(8.8) 1.23263(6) 1.8720.0204 0.06 (Ca_(2.94)Co_(0.06))Al₂(SiO₄)_(0.8)(OH)_(8.8) 1.23231(7)1.871 0.0238 0.07 (Ca_(2.93)Co_(0.07))Al₂(SiO₄)_(0.8)(OH)_(8.8)1.23196(6) 1.869 0.0273 0.08(Ca_(2.92)Co_(0.08))Al₂(SiO₄)_(0.8)(OH)_(8.8) 1.23162(12) 1.868 0.03090.09 (Ca_(2.91)Co_(0.09))Al₂(SiO₄)_(0.8)(OH)_(8.8) 1.23141(13) 1.8670.0344 0.10 (Ca_(2.90)Co_(0.10))Al₂(SiO₄)_(0.8)(OH)_(8.8) 1.23131(10)1.866

The relationship between the products and the heating temperature wasfurther examined by XRD for (Ca_(2.9)Co_(0.1))Al₂(SiO₄)_(0.8)(OH)_(8.8),which revealed that there was no change (remained as(Ca_(2.9)Co_(0.1))Al₂(SiO₄)_(0.8)(OH)_(8.8)) from room temperature up to300° C., but heating at 350° C. resulted in a change intoaluminosilicate hydroxide (Ca₁₂Al₁₀Si₄O₃₂(OH)₆), unslaked lime (CaO),and cobalt oxide (Co₃O₄). The products of heating at over 350° C. werealuminosilicate hydroxide, unslaked lime, and cobalt oxide in everycase. When the heating was performed at over 700° C., thealuminosilicate hydroxide was further dehydrated into anhydrousaluminosilicate (Ca₁₂Al₁₀Si₄O₃₅).

Table 2 shows the specific surface area and the cobalt oxide particlesize when four types of cobalt-containing hydrogarnet were synthesizedwith different Co/Ca ratios of 0.0169, 0.0238, 0.0344, and 0.0714, andthen heated at 400° C. The specific surface area was at its maximum of6.5 m²/g when the hydrogarnet had a Co/Ca ratio of 0.0344, and was about2 to 3 m²/g with other hydrogarnets. Meanwhile, the cobalt oxideparticle size was substantially the same as the 250 to 275 Å ofcobalt-containing hydrogarnet with a Ca/Co ratio of from 0.0169 to0.0344, and increased to 850 Å at Co/Ca=0.0714. A larger cobalt oxideparticle size is undesirable because it leads to a decrease indispersibility, that is, a decrease in catalyst activity, so theparticle size of the cobalt oxide needs to be as small as possible.

TABLE 2 Specific surface area and cobalt oxide particle size of fourtypes of cobalt-containing hydrogarnet (with different Co/Ca ratios of0.0169, 0.0238, 0.0344, and 0.0714) after heating at 400° C. Co/Ca0.0169 0.0238 0.0344 0.0714 X 0.05 0.07 0.10 — Specific surface area 1.92.8 6.5 2.9 (m²/g) Co₃O₄ particle size (Å) 250 260 275 850

Table 3 shows the relationship of specific surface area and cobalt oxideparticle size to the heating temperature of cobalt-containinghydrogarnet with a Co/Ca ratio of 0.0344. The specific surface area wasroughly the same (5.7 and 6.5 m²/g) after heating at 350 and 400° C.,but decreased steadily after heating at 450° C. and above. Meanwhile,the cobalt oxide particle size was roughly the same (260 and 275 Å)after heating at 350 and 400° C., but increased steadily from 447 Åafter heating at 450° C. and above. The above results indicate that aCo/Ca ratio of 0.0344 and a heating temperature of 400° C. or lower arepreferable for manufacturing an aluminosilicate catalyst supportingcobalt oxide.

TABLE 3 Specific surface area, cobalt oxide particle size, and heatingtemperature of cobalt-containing hydrogarnet with Co/Ca of 0.0344.Heating temp. (° C.) 350 400 450 500 600 Specific surface area (m²/g)5.7 6.5 4.2 3.5 2.4 Co₃O₄ particle size (Å) 260 275 447 489 856

We will now describe the method for examining the catalytic activity ofthe aluminosilicate catalyst supporting cobalt oxide. The reactionapparatus was a normal pressure, compact, fixed bed, flow through type.The catalyst particle size was 300 to 500 μm, the reaction temperaturewas from room temperature to 500° C., three types of reaction gas(propylene, benzene, and toluene) were used, the reaction gasconcentration was 1000 ppm, the flow-through gas was air, the gas fluxwas 100 mL/min, the space velocity was 10,000 h⁻¹, and gas analysis wasperformed by gas chromatography (packing material: Porapak P, 5Amolsieve, activated carbon, column: 2 m×3). FIG. 10 shows therelationship between the Co/Ca ratio, the specific surface area, and thedecomposition rate of each gas (propylene, benzene, and toluene) whenusing an aluminosilicate catalyst supporting cobalt oxide andmanufactured by heating at 400° C. The decomposition rate was found tobe closely correlated to the specific surface area, and with all thereaction gases, the maximum decomposition rate was exhibited with acatalyst whose Co/Ca ratio was 0.0344((Ca_(2.9)Co_(0.1))Al₂(SiO₄)_(0.8)(OH)_(8.8)).

FIG. 11 shows the results of subjecting propylene to oxidativedecomposition at various reaction temperatures using(Ca_(2.9)Co_(0.1))Al₂(SiO₄)_(0.8)(OH)_(8.8) as the catalyst. Thedecomposition rate was 2% at a reaction temperature of 200° C., but thedecomposition rate rose along with temperature, reaching 100% at 325° C.The product after decomposition was only CO₂. H₂O was produced, but wasnot analyzed. Meanwhile, with a catalyst not substituted with cobalt,that is, just an aluminosilicate, the decomposition rate was zero at areaction temperature of 325° C., was 2% at 400° C., and reached 100% at625° C. When a self-combustion experiment was conducted without using acatalyst, propylene began burning only when heated to at least 600° C.The above results mean that it is possible to lower the combustiontemperature by using an aluminosilicate as a catalyst, and that thecatalytic activity of an aluminosilicate increases by about 200° C. whenpart of its calcium is substituted with cobalt, and the presentinvention makes it possible to realize even lower temperatures in theseoxidative decomposition reactions. The catalyst of the present inventionis useful as an oxidation catalyst for the oxidative decomposition ofvolatile organic compounds, hydrocarbons, and other such materials to betreated.

An aluminosilicate catalyst supporting cobalt oxide that has the abovefeatures can be obtained as a powder in the manufacturing methodthereof. In addition to utilizing this substance as a powder, many otherconveniences and new functions as a molded article will likely berealized. The form of the molded article will be determined by theintended use, and the molding method can be any one that is used in themanufacture of molded ceramics. Possible forms of the molded articleinclude pellets, granules, a sheet, a rod, a tube, hollow fibers, amonolith, and a honeycomb, and examples of molding methods includecasting, press molding, dry CIP molding, injection molding, and sheetmolding. Naturally, whether the molded article will be solid or porousis taken into account along with the desired form in molding.

FIG. 12 is a simplified view of an example of the measurement apparatusused to examine the oxidation catalyst performance of the substance ofthe present invention. This apparatus consists of (1) a gas supply unit,(2) a heating unit, and (3) a gas analysis unit. The gas supply unitsupplies the hydrocarbons to be subjected to oxidative decomposition,and the air or oxygen used as a combustion auxiliary. The heating unitheats a reaction tube filled with the sample to a specific temperature.The gas analysis unit analyzes the composition of the supply gas thathas passed through the sample. The reaction tube is modified accordingto the form of the sample, and FIG. 13 shows a simplified examplethereof. For a sample in the form of a powder, pellets, or granules (4),the center of a silica glass reaction tube (5) is packed with thesample, and the ends of the sample are held in place with rock wool (6).For a sample in the form of a sheet (7), the ends of the sheet are heldin place with silica glass tubes (8) via a sealant, and the silica glasstubes are fixed to the sample sheet.

The function of an aluminosilicate catalyst supporting cobalt oxide thatis in the form of a molded article was examined for propylene, benzene,and toluene, for example, which revealed that all of these hydrocarbonsare decomposed at a temperature of 200° C. or higher. The decompositionrate thereof was comparable to that with a powder.

The present invention relates to an aluminosilicate catalyst supportingcobalt oxide, and to a method for manufacturing this catalyst, and withthe present invention, 1) it is possible to provide a catalyst withhigher activity than conventional oxidation or combustion catalysts, 2)higher oxidation capability can be achieved at lower temperatures thanwith conventional catalysts, 3) an aluminosilicate catalyst supportingcobalt oxide can be manufactured by a simple process under lowertemperature conditions (at least 300° C. and no higher than 1000° C.),and 4) this catalyst is useful as a way to oxidatively decomposevolatile organic compounds and the like.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the ESR measurement results for Ca₁₂Al₁₀Si₄O₃₅ at roomtemperature;

FIG. 2 shows the results of Raman spectroscopy for Ca₁₂Al₁₀Si₄O₃₅ atroom temperature;

FIG. 3 shows the crystal structure of Ca₁₂Al₁₀Si₄O₃₅;

FIG. 4 shows the relationship between reaction time and the propylenedecomposition rate under a nitrogen atmosphere (a) using Ca₁₂Al₁₀Si₄O₃₅as the catalyst (air was introduced (b) 220 minutes after the start ofthe reaction, the active oxygen consumed in the Ca₁₂Al₁₀Si₄O₃₅ wasregenerated, and the oxidative decomposition of propylene in a nitrogenatmosphere was recommenced);

FIG. 5 is a simplified view of the measurement apparatus used to examinethe oxidation catalyst performance;

FIG. 6 shows a simplified diagram of the shape of the reaction tube;

FIG. 7 shows the Raman spectroscopy results for Ca₁₂Al₁₀Si₄O₃₅ after apropylene decomposition experiment in a nitrogen atmosphere;

FIG. 8 shows the XRD results for cobalt-containing hydrogarnetsynthesized at various Co/Ca ratios from 0 to 0.0714;

FIG. 9 shows the relationship between lattice constant and Co/Ca ratiofor cobalt-containing hydrogarnet synthesized at various Co/Ca ratiosfrom 0 to 0.0714;

FIG. 10 shows the relationship between the Co/Ca ratio, the specificsurface area (black diamonds), and the decomposition rate of variousgases (propylene (white circles), benzene (black squares), and toluene(black triangles)) at a reaction temperature of 300° C. when using analuminosilicate catalyst supporting cobalt oxide;

FIG. 11 shows the results of subjecting propylene to oxidativedecomposition at various reaction temperatures using(Ca_(2.9)Co_(0.1))Al₂(SiO₄)_(0.8)(OH)_(8.8) as the catalyst;

FIG. 12 is a simplified view of the measurement apparatus used toexamine the oxidation catalyst performance;

FIG. 13 shows a simplified diagram of the shape of the reaction tube;

FIG. 14 shows the results of subjecting benzene to oxidativedecomposition at various reaction temperatures usingCa_(2.9)Co_(0.1))Al₂(SiO₄)_(0.8)(OH)_(8.8) as the catalyst; and

FIG. 15 shows the results of subjecting toluene to oxidativedecomposition at various reaction temperatures usingCa_(2.9)Co_(0.1))Al₂(SiO₄)_(0.8)(OH)_(8.8) as the catalyst.

LIST OF ELEMENTS

(FIG. 5)

1 gas supply unit

2 heating unit

3 gas analysis unit

(FIG. 6)

4 sample in the form of powder, pellets, or granules

5 silica glass reaction tube

6 rock wool

7 sheet-form sample

8 silica glass tube

(FIG. 12)

1 gas supply unit

2 heating unit

3 gas analysis unit

(FIG. 13)

4 sample in the form of powder, pellets, or granules

5 silica glass reaction tube

6 rock wool

7 sheet-form sample

8 silica glass tube

BEST MODE FOR SUPPORTING OUT THE INVENTION

The first aspect of the present invention will now be described inspecific terms by giving examples, but the present invention is notlimited in any way by the following examples.

EXAMPLE 1

0.77 g of unslaked lime (as a calcia source), 1.8 g of alumina sol (asan alumina source; containing 20% Al₂O₃), and 0.21 g of amorphous silica(as a silica source) were weighed out, and water was added to bring thetotal volume up to 14.6 mL. The mixture (suspension) thus prepared wasput in an autoclave with a capacity of 25 mL, and heated for 15 hours at200° C. while being stirred at 25 rpm. The system was then allowed tocool to room temperature, filtered, and dried, which gave hydrogarnetexpressed by the compositional formula Ca₃Al₂(SiO₄)_(0.8)(OH)_(8.8).This hydrogarnet was heated for 5 hours at 700° C. in an electricfurnace under an air atmosphere, which gave Ca₁₂Al₁₀Si₄O₃₅ (a novelactive oxygen developing substance). FIGS. 1 and 2 show the ESR andRaman spectroscopy results at room temperature for the Ca₁₂Al₁₀Si₄O₃₅produced by this method. As discussed above, Ca₁₂Al₁₀Si₄O₃₅ wasconfirmed to include or occlude active oxygen in its structure.

EXAMPLE 2

1.0 g of Ca₁₂Al₁₀Si₄O₃₅ that had been molded into pellets with a size of300 to 500 μm was packed into a quartz glass reaction tube that had beenplaced in an electric furnace, and the reaction tube temperature was setto the desired temperature between 200 and 900° C. A mixed gas of airand propylene was introduced into the reaction tube at a flux of 100mL/min. The propylene concentration was 1000 ppm. The outlet gas fromthe reaction tube was introduced to a gas chromatograph, and the gas wasanalyzed. No decomposition of propylene was noted between 200 and 375°C., but 2% decomposition was noted at 400° C. The decomposition raterose along with the reaction temperature, reaching 50% at 500° C., 95%at 550° C., and 100% at over 600° C. The only gases produced by thedecomposition of the propylene were CO₂ and H₂O, indicating that apropylene oxidative decomposition reaction had occurred.

EXAMPLE 3

1.0 g of Ca₁₂Al₁₀Si₄O₃₅ that had been molded into pellets with a size of300 to 500 μm was packed into a quartz glass reaction tube that had beenplaced in an electric furnace, and the reaction tube temperature was setto the desired temperature between 200 and 900° C. A mixed gas of airand benzene was introduced into the reaction tube at a flux of 100mL/min. The propylene concentration was 1000 ppm. The outlet gas fromthe reaction tube was introduced to a gas chromatograph, and the gas wasanalyzed. No decomposition of benzene was noted between 200 and 400° C.,but 3% decomposition was noted at 425° C. The decomposition rate rosealong with the reaction temperature, reaching 10% at 450° C., 37% at500° C., 86% at 550° C., 98% at 600° C., and 100% at over 625° C. Theonly gases produced by the decomposition of the benzene were CO₂, CO,and H₂O, indicating that a benzene oxidative decomposition reaction hadoccurred.

EXAMPLE 4

1.0 g of Ca₁₂Al₁₀Si₄O₃₅ that had been molded into pellets with a size of300 to 500 μm was packed into a quartz glass reaction tube that had beenplaced in an electric furnace, and the reaction tube temperature was setto 600° C. A mixed gas of nitrogen and propylene was introduced into thereaction tube at a flux of 50 mL/min. The propylene concentration was100 ppm. The outlet gas from the reaction tube was introduced to a gaschromatograph, and the gas was analyzed. The relationship betweenpropylene decomposition rate and reaction time was measured. Theseresults are shown in FIG. 4. The initial decomposition rate was 80%, butthis decreased over time, dropping to 0% after 120 minutes, after whichno oxidative decomposition of propylene occurred. FIG. 7 shows the Ramanspectroscopy results for the active oxygen in Ca₁₂Al₁₀Si₄O₃₅ obtainedafter propylene decomposition in a nitrogen atmosphere at variousreaction times. The active oxygen in the structure decreased as thecombustion of the propylene proceeded. Furthermore, it was confirmedthat the active oxygen was regenerated in the structure by exposing theCa₁₂Al₁₀Si₄O₃₅ that had lost its active oxygen to air at 400° C. orhigher. It was shown that the active oxygen in the lattices consumed bythe oxidation reaction was regenerated by taking in oxygen from the air,allowing the propylene to burn continuously.

EXAMPLE 5

Ca₁₂Al₁₀Si₄O₃₅ that had been molded into a porous sheet with thicknessof 2.0 mm and a diameter of 10 mm was sandwiched between quartz glassreaction tubes with a diameter of 10 mm, this assembly was placed in anelectric furnace, and the sample temperature was raised to the desiredtemperature between 200 and 700° C. A mixed gas of air and propylene wasintroduced into the reaction tube at a flux of 30 mL/min. The propyleneconcentration was 500 ppm. The outlet gas from the reaction tube wasintroduced to a gas chromatograph, and the gas was analyzed. Nodecomposition of propylene was noted between 200 and 375° C., but 3%decomposition was noted at 400° C. The decomposition rate rose alongwith the reaction temperature, reaching 60% at 500° C. and 100% at over600° C. The only gases produced by the decomposition of the propylenewere CO₂ and H₂O, indicating that a propylene oxidative decompositionreaction had occurred.

EXAMPLE 6

Measurements were made under the same conditions as in Example 5, butchanging the type of gas to methane. Decomposition began at a reactiontemperature of 450° C., after which the relationship between methanedecomposition rate and reaction temperature was 5% at 500° C., 45% at600° C., and 100% at 700° C.

EXAMPLE 7

A mix was prepared by mixing 25 weight parts ketjen black (as aconductive material) and 5 weight parts Teflon® (as a binder) into 70weight parts Ca₁₂Al₁₀Si₄O₃₅. The mix was press molded on the surface ofan aluminum foil collector with a thickness of 22 μm, producing a sheetwith a thickness of 50 μm, and this sheet was then punched out in adiameter of 15 mm to produce a disk-shaped electrode. This electrode wasdisposed across from a disk of metallic lithium with a thickness of 0.1mm and a diameter of 15 mm, and a piece of nonwoven cloth with athickness of 100 μm was disposed as a separator between the electrodeand the metallic lithium. A solution produced by dissolving 1 mol ofLiPF₆ in a mixed solvent of ethylene carbonate and diethyl carbonate(3:7 volumetric ratio) was used for the electrolyte. A cell was producedby sandwiching these components between sheets of Teflon®. Current wasallowed to flow into the cell at 0.1 mA/cm² up to 4.5 V, after which theelectrode was recovered. The composition of the electrode material wasanalyzed after the material was washed with diethyl carbonate, whichrevealed it to be Li₃₀ Ca₁₂ (Al_(14−X)Si_(X))_(33+0.5X).

Next, the second aspect of the present invention will now be describedin specific terms by giving examples, but the present invention is notlimited in any way by the following examples.

EXAMPLE 8

0.77 g of unslaked lime (as a calcia source), 0.033 g of cobalthydroxide (Co(OH)₂; as a cobalt source), 1.8 g of alumina sol (as analumina source; containing 20% Al₂O₃), and 0.21 g of amorphous silica(as a silica source) were weighed out, and water was added to bring thetotal volume up to 14.6 mL. The mixture (suspension) thus prepared wasput in an autoclave with a capacity of 25 mL, and heated for 15 hours at200° C. while being stirred at 25 rpm. The system was then allowed tocool to room temperature, filtered, and dried, which gavecobalt-containing hydrogarnet expressed by the compositional formula(Ca_(2.9)Co_(0.1))Al₂(SiO₄)_(0.8)(OH)_(8.8). This cobalt-containinghydrogarnet with the compositional formula of(Ca_(2.9)Co_(0.1))Al₂(SiO₄)_(0.8)(OH)_(8.8) was heated for 5 hours at400° C., which gave an aluminosilicate catalyst supporting cobalt oxide.

FIG. 11 shows the results when the oxidative decomposition of propylenewas carried out at various reaction temperatures using analuminosilicate catalyst supporting cobalt oxide. The catalyst reactionexperiment was conducted as follows. The reaction apparatus was a normalpressure, compact, fixed bed, flow through type, the catalyst particlesize was 300 to 500 μm, the reaction temperature was from roomtemperature to 500° C., the reaction gas concentration was 1000 ppm, theflow-through gas was air, the gas flux was 100 mL/min, the spacevelocity was 10,000 h⁻¹, and gas analysis was performed by gaschromatography (packing material: Porapak P, 5A molsieve, activatedcarbon, column: 2 m×3). As a result, the decomposition rate was 2% at areaction temperature of 200° C., but the decomposition rate rose alongwith temperature, reaching 100% at 325° C. The product afterdecomposition was only CO₂. H₂O was produced, but was not analyzed.

EXAMPLE 9

A catalyst experiment was conducted by the same method as in Example 8,using an aluminosilicate catalyst supporting cobalt oxide prepared bythe same method as in Example 8. FIG. 14 shows the results of subjectingbenzene to oxidative decomposition at various reaction temperatures. Thedecomposition rate was 0% at a reaction temperature of 200° C. and 13%at 225° C., but the decomposition rate rose along with temperature,reaching 100% at 300° C. The product after decomposition was only CO₂.H₂O was produced, but was not analyzed.

EXAMPLE 10

A catalyst experiment was conducted by the same method as in Example 8,using an aluminosilicate catalyst supporting cobalt oxide prepared bythe same method as in Example 8. FIG. 15 shows the results of subjectingtoluene to oxidative decomposition at various reaction temperatures. Thedecomposition rate was 0% at a reaction temperature of 225° C. and 25%at 250° C., but the decomposition rate rose along with temperature,reaching 100% at 325° C. The products after decomposition were CO₂ andbenzene. H₂O was produced, but was not analyzed.

INDUSTRIAL APPLICABILITY

As detailed above, the present invention relates to an aluminosilicatehaving a zeolite-like structure in which active oxygen (superoxide: O₂⁻, peroxide: O₂ ²⁻) is encapsulated, that is, a novel active oxygendeveloping substance, and to a molded article of this substance. Theactive oxygen included or occluded in the structure of this substanceinduces hydrocarbon oxidation reactions (such as epoxidation, completeoxidation, partial oxidation, and coupling), and the novel active oxygendeveloping substance of the present invention can be utilized in a widerange of technological fields dealing with the environment, energy, thechemical industry (manufacturing process), and so forth. Further, amolded article of inorganic compound of the present invention is useful,for example, as an exhaust gas purification catalyst for two-wheeledvehicles, a solid electrolyte for secondary cells, an oxygen occlusioncarrier, or the like.

The present invention further relates to an aluminosilicate catalystsupporting cobalt oxide, and to a method for manufacturing thiscatalyst, and the present invention provides a catalyst with higheractivity than conventional oxidation or combustion catalysts. The actionof the active oxygen included or occluded in the structure of thealuminosilicate results in a higher oxidation capability at lowertemperatures than conventional catalysts. An aluminosilicate catalystsupporting cobalt oxide can be manufactured by a simple process underlower temperature conditions (at least 300° C. and no higher than 1000°C.). This catalyst is useful as a way to oxidatively decompose volatileorganic compounds and the like.

1. An inorganic compound that has an active oxygen developing mechanismand includes or occludes active oxygen, the inorganic compound includesor occludes both a superoxide anion (O₂−) and a peroxide anion (O₂ ²⁻),wherein the inorganic compound is an aluminosilicate obtained by thepyrolysis of hydrogarnet, and wherein the compositional formula of thealuminosilicate is Ca₁₂(Al_(14−X)Si_(X))O_(33+0.5X), where the value ofX is in the range of 0<X≦4.
 2. A method for manufacturing the inorganiccompound defined in claim 1, wherein an aluminosilicate having an activeoxygen developing mechanism is manufactured by heating hydrogarnet at nolower than 700° C. and no higher than 1200° C. and wherein thecompositional formula of the hydrogarnet is Ca₃Al₂(SiO₄)_(3−Y)(OH)_(4Y),where the value of Y is in the range of 0≦Y<3.
 3. An oxidation catalystcomposed of the inorganic compound according to claim 1 or a moldedarticle thereof.
 4. A member composed of a molded article of theinorganic compound according to claim
 1. 5. The member according toclaim 4, wherein the member is an exhaust gas purification catalyst. 6.The member according to claim 4, wherein the member is a solidelectrolyte.
 7. The member according to claim 4, wherein the member isan oxygen occlusion carrier.
 8. An aluminosilicate catalyst supportingcobalt oxide, which is an oxidation or combustion catalyst containing asa constituent component an aluminosilicate that includes or occludesactive oxygen in its structure, wherein the cobalt oxide is carried onthe aluminosilicate surface and wherein the aluminosilicate has acompositional formula of Ca₁₂(Al_(14−X)Si_(X))O_(33+0.5X), where thevalue of X is in the range of 0≦X≦4.
 9. A method for manufacturing thealuminosilicate catalyst supporting cobalt oxide according to claim 8,wherein cobalt-containing hydrogarnet is decomposed by heating andwherein the cobalt-containing hydrogarnet has a compositional formula of(Ca_(3−Y)CO_(Y))Al₂(SiO₄)_(3−Z)(OH)_(4Z), where the value of Y is in therange of 0<Y≦0.1, and Z in the range of 0≦Z≦2.2.
 10. The method formanufacturing an aluminosilicate catalyst supporting cobalt oxideaccording to claim 9, wherein the cobalt-containing hydrogarnet isheated at no lower than 300° C. and no higher than 1000° C.
 11. A membercomposed of a molded article of the cobalt oxide aluminosilicatecatalyst according to claim
 8. 12. The member according to claim 11,wherein the member is an exhaust gas purification catalyst for atwo-wheeled vehicle.
 13. The member according to claim 11, wherein themember is a combustion exhaust gas purification catalyst.
 14. The memberaccording to claim 11, wherein the member is an oxygen occlusion member.